The investment comes as UnitedHealth faces soaring medical costs, federal investigations, the fallout of the killing of a top executive and a cyberattack last year.

Key Takeaways Buffett has long been a big proponent of the index funds that Bogle helped bring to the masses.However, his public declaration that Bogle is an American hero may have also been influenced by the fact that one of Bogle's funds just helped Buffett win a $1 million bet.